1. Field of the Invention
The present invention generally relates to connection systems for cables, and more particularly to a distribution frame system used to cross-connect and interconnect optical fibers used in telecommunications, the system providing improved management of jumper cables as well as storage and interconnection of fibers on a given tray.
2. Description of the Prior Art
In the past several years, optical fibers have become the preferred medium, over copper wire, for carrying telecommunications signals. Cable management is quite different with optical fibers as opposed to copper wiring, particularly due to the signal losses which can occur when an optical fiber is bent or otherwise damaged. Distribution systems for optical fibers have been devised to minimize such losses. For example, U.S. Pat. No. 5,093,887 discloses a cabinet having a front panel and several shelves which slide out the front, each of the shelves supporting one or more splice trays (splice trays may also be accessible front the back plane of frame, as described in U.S. Pat. No. 5,241,617). Incoming and outgoing fibers pass through cutouts formed in the back, bottom or top walls of the cabinet. Clips are used to retain the fibers on the trays with an appropriate minimum bend radius, and a pivoting support arm is used with each shelf to also minimize bending stress to the fibers
In U.S. Pat. No. 4,792,203, storage trays mounted along the left and right inner sides of the cabinet pivot outwardly through the front access plane. The trays are designed to provide separate pathways for the storage of slack from three interconnected fibers, namely, the trunk fiber, the pigtail (or jumper) fiber, and the distribution fiber.. The trunk and distribution fibers exit through cutouts formed in the side walls of the cabinet.
U.S. Pat. No. 5,067,784 shows a similar design in which trays are also mounted along the left and right inner sides of the cabinet, but they slide out rather than pivot. Provision is made for jumper cables to cross from a tray on one side of the cabinet to a tray on the other side. Surplus slack in the jumper is allowed to hang in a central area of the cabinet. Each of the trays has a mounting region or bulkhead for receiving interconnected pairs of optical fiber connectors, and a region behind the bulkhead for storing excess slack from the fibers which exit at the back of the tray. A hinged plate covers this rear area. The fibers which are connected to the front of the bulkhead exit the tray in an arcuate extension located at the front corner of the tray. Curved vanes are used to limit the minimum bend radius of the fibers which undergo a 90.degree. bend from the bulkhead to the arcuate extension.
A similar connector tray is illustrated in U.S. Pat. No. 5,071,211. In that construction, however, the forwardmost portion of the tray is hinged and movable downward to facilitate access to the front portion of the bulkhead.
Another fiber optic distribution system, described in U.S. Pat. No. 4,824,196, has several modules or drawers pivotally attached to the inside of a cabinet. A smaller splice tray with separation pages may be attached to the drawer, behind the bulkhead. The bulkhead may be of a stair-step or zig-zag shape, whereby the forward-exiting fibers do not have to undergo as large a bend angle, and also allows the width of the drawer to be shorter. The forwardmost portion of the drawer forms a door which again hinges downwardly.
As further taught in U.S. Pat. No. 5,247,603, the trays may be designed for cross-connection (use of a jumper) or interconnection (no jumper). The disclosed construction places the trays in a page array wherein each tray can be held in one of three access positions. That patent discusses and cites several other references of general relevance to distribution systems and connector trays.
While the foregoing designs address some aspects of fiber optic cable management, they have proven inadequate for the increasingly demanding standards in such systems. For example, they must be able to accommodate transmission rates of up to 2 Gb with acceptable bit-error rates. It is also believed that jumper fibers should now be two meters or more in length to minimize modal noise. In existing distribution systems, the surplus slack from jumper cables of this length must be wound excessively around the various posts and walls, and tend to bind or otherwise make the fibers more difficult to handle. These systems do not adequately address the management of very long jumpers for (i) interconnection of a pair of fibers each terminated in the same drawer or cabinet, (ii) interconnection of a pair of fibers whose ends terminate in different cabinets, but in the same bay of a distribution frame, or (iii) interconnection of a pair of fibers whose ends terminate in different bays of a multibay distribution frame.
In addition to inadequacies in the management of jumper cables, prior art distribution systems can also use improvement in the storage and interconnection of fibers on a given drawer or tray. For example, in the construction shown in U.S. Pat. No. 5,067,78, while the vanes are useful in maintaining fiber radius against pulling forces, the back side of the vanes can actually cause severe bending of the fiber if the connector has an extended boot or grip. Several conventional connectors have such boots which extend all the way to, and contact the back side of, the vanes, inducing microbends in the fiber. Indeed, comparison of this design with that depicted in U.S. Pat. No. 5,071,211 (FIG. 23) reveals that the vanes must be completely removed in order for the front of the tray to accommodate the longer boots, yet there is still undue bending of the fibers where they contact the forwardmost wall of the tray. It would, therefore, be desirable to devise a fiber optic distribution system which can better control the minimum bend radius of stored and interconnected fibers on a given tray, as well as properly manage surplus jumper cable, whether it is an intracabinet, intrabay or interbay cable. It would be further advantageous to provide a construction which allows for back plane access through the front panel of the cabinet.